ext3 is a robust, time-tested file system used in many computers and NAS devices usually running Linux. ext4 is a newer version that uses very different data storage schemes.
The migration from ext3 to ext4
will happen over the course of many years.

You can use File Scavenger™ to recover data from an ext volume when it becomes corrupted or is accidentally deleted.
In these situations the file system metadata is still intact and recovery is possible.

Raw recovery is possible for an ext4 volume when a file is deleted or the volume is reformatted.

In these situations the file system metadata is zeroed out.
In some cases our experienced data recovery engineers can use
file carving techniques to recover all or part of the data. In other cases data is unrecoverable.

UFS1 and UFS2 are less popular file systems. They use data storage schemes similar to ext3, therefore affording similar recovery options and possibilities.